The present invention relates to a method of releasing metals from catalysts using dentrifying bacteria. It relates in particular to the regeneration of spent catalysts and to the recovery of metals from catalysts, especially molybdenum and nickel.
Catalysts are used in a variety of hydrocarbon treatment and conversion processes, such as in the cracking of petroleum residues and in the processing of other chemicals. During use of the catalyst, metal sulfides, metal oxides and organometallic compounds are deposited on the surface and in the pores of the catalysts, causing a loss of catalytic activity and selectivity. This leads to poor product distribution and otherwise reduces the effectiveness of the catalyst. This is particularly so when crude oils containing high amounts of certain metals are to be processed.
Attempts have been made to identify bacteria having the ability to regenerate spent catalysts contaminated with metals. U.S. Pat. No. 3,414,524 describes a method of activating or reactivating inactive catalytic material using sulfate-reducing, sulfate-oxidizing and iron oxidizing bacterial strains. The method is particularly used to reactivate catalysts poisoned by exposure to sulfur.
U.S. Pat. No. 4,559,313 relates to the removal from catalyst of inorganic contaminants, particularly vanadium and nickel. The method uses an oxidizing, i.e., aerobic, species of bacteria. Suitable bacteria are selected from the group consisting of Ferrobaccillus ferrooxidans, Thiobacillus ferrooxidans, (now considered to be the same organism), Thiobacillus thiooxidans, and Sulfolobous acidolphus, with Thiobacillus ferroxidans being particularly preferred. This latter bacterium, however, is impractical for industrial applications. Because these bacteria are very sensitive to tungstate and molybdate, the process requires unacceptably large volumes and is very slow. The other species mentioned in U.S. Pat. No. 4,559,313 do not effectively remove metals from spent catalyst. In addition, all of the species disclosed require oxygen for metabolism.